Thermal expansion of La-based BMG studied by in situ high-energy X-ray diffraction

The present work focuses on the study of the thermal stability of La62Al14(Cu5/6Ag1/6)14Ni5Co5 (at.%) bulk metallic glass (BMG) using the state-of-the-art high temperature in situ hard X-ray scattering techniques available at the undulator beamline ID11 of ESRF (Grenoble, France). Constant-rate heating experiments using a fast X-ray camera (time resolution of 3 s) reveal detailed information about the thermal stability of the La-based BMG. Analyzing diffraction patterns in a reciprocal space yields thermal expansion of amorphous alloy providing insight about the thermally activated relaxation effects and glass transition. We found that in the region 20 K below the glass transition (Tg = 420 K) thermal expansion curve exhibits negative slope which indicates annealing-out of the quenched-in free volumes. The glass transition appears as a brake in the value of coefficient of the volume thermal expansion αth. Furthermore, real space analysis based on reduced pair distribution function G(r) allows to trace the changes in the local atomic structure of amorphous material during constant-rate heating.